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Two-dimensional liquid cell dielectric microscopy

Periodic Reporting for period 1 - Liquid2DM (Two-dimensional liquid cell dielectric microscopy)

Reporting period: 2019-10-01 to 2021-03-31

This project develops a new imaging technology capable of imaging and determining for the first time electric polarization and electrodynamic properties of molecular liquids under confinement on the molecular and atomic scale. These are fundamental physical properties (represented by the dielectric constant or electric permittivity) that describe how matter polarizes in response to an external electric field and, in turn, determine fundamental forces that govern molecular interactions. In practice, they play a crucial role in molecular organization, structuring and functioning. As such, they impact in a wide range of phenomena in a variety of fields, from physical sciences to chemistry and biology. Examples include surface coating and wettability; solid-liquid transitions; water-mediated adsorption and transport of charged ions and molecules; molecular binding; and chemical reactions. Despite their impact, our understanding of these properties has remained limited to macroscopic systems in which molecular information associated to molecular heterogeneities and interfacial effects average out. This is due to the lack of experimental tools able to access them directly on the molecular and atomic scale.
In the last decade, we pioneered the development of Scanning Dielectric Microscopy (SDM), succeeding in probing electric polarization properties of nano-objects and macromolecules as small as few tens of nanometers in size. We achieved that by using the scanning probe microscopy approach – using a nanosized scanning tip as a probe - and through a series of instrumental breakthroughs, which pushed the spatial resolution of standard dielectric spectroscopy from micrometer scale down to the nanoscale. The challenge is now to push the technique down to the atomic level. This is exactly what this project will do.
The overall objective is to push the boundaries of SDM to probe electric polarization and electrodynamics properties of molecular liquids under confinement, with focus on water, electrolytic solutions and biologically relevant molecules, by implementing novel experimental and theoretical approaches. In particular, we will engineer 2D liquid cells made of van der Waals crystals by exploiting the most advanced 2D-materials technology, and we will directly probe the molecular liquids confined inside using the SDM scanning probe.
In the first 18 months, the team has been developing the main microscopic setups and tools required for the project and has started the experiments on confined molecular liquids, as scheduled. This was achieved despite the impact of the Covid-19 pandemic, which reached the UK after just 5 months and impeded the access to the team’s lab for around 6 months. Thanks to the contingency plan in place, the team managed to minimize the pandemic disruptions. The team comprises 2 postdoctoral researchers and 1 postgraduate researcher, who joined the group of the principal investigator during this period.
A new lab space dedicated to this project has been set up, where the newly developed setups have been installed. One setup has been implemented and tested in this period, and it is operational. It has been designed for the study of electric polarization and electrodynamic properties of nanoconfined water solutions. A second setup for the study of confined biomolecules, which includes more technical advances, is currently under development. It is expected to be completed in the upcoming months, as planned.
First 2D liquid cells made of various 2D crystals were successfully fabricated by the team for the measurement of confined water solutions. Two different designs have been implemented by transferring and stacking 2D crystals and using microfabrication techniques: in the first one, water is trapped in 2D nanoenclosures, while in the second one it fills into 2D nanochannels with controlled thickness. The team has started the dielectric microscopy experiments of these devices, as scheduled, and the analysis of the obtained data is in progress. More devices and results will be produced in the months to come.
The PI disseminated results related to this project in several peer-review publications and invited talks at international workshops/conferences and on social media.
We are developing a new microscopy platform able to visualize key physical properties of molecular liquids that has remained unknown so far and with unprecedented resolution. To our knowledge, currently there is no other research group able to achieve that world-wide. This is achieved by combining two advanced technologies: a novel scanning probe microscopy technique and the 2D-materials technology available in our group in Manchester. We are applying it to the study of water solutions and biomolecules of major significance in materials and life sciences, but it could also be apply to the study of other molecular liquids.
The first setup that we have developed in these first months of the project has already provided experimental data that are much needed to understand water polarization/electrodynamic properties and water-mediated interactions. Work is in progress to interpret our results and we expect to be able to provide better theoretical models by the end of the project. Despite the advances in atomistic simulations, theorists struggle to predict them. Our experimental data are being key to benchmark their models. In turn, they will help our understanding of the physics of nanoconfined molecular liquids, which is important for developing novel devices for electrochemistry, energy storage and analytical applications.
As the project is now progressing smoothly, we expect to start the experiments on biomolecules in a few months, as planned. By the end of the project, we should be able to provide experimental data of electric polarization/dynamic properties of single biomolecules such as proteins and DNA that are crucial in life sciences.
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